Method of incremental cold forming an angled corner in a continuous sheet of advanced high strength metal

ABSTRACT

An outer bend radius is cold formed in an outer position within a final arc of the angled corner with an outer bend radius male die member. A central bend radius is cold formed in a central position spaced from the outer position and within the final arc of the angled corner with a central bend radius male die member. An inner bend radius is cold formed in an inner position that is spaced from the outer and central positions and the inner position is within a final arc of the angled corner with an inner bend radius male die member. The angled corner is transferred between each of the bend radii male die members using a continuous advanced high strength metal sheet in which the angled corner is formed.

FIELD

The present disclosure relates to cold forming of metal sheets that have low cold forming formability.

BACKGROUND

Advanced high strength metals typically have poor ductility or formability. Newer advanced high strength metals, such as ultra-high strength steels and 7000 series aluminum alloys, have been developed for lightweighting purpose with somewhat improved ductility. Nevertheless, the formability of these newer advanced high strength metals is typically not sufficient to permit successful cold forming of desired shapes using traditional forming methods and dies. Such traditional cold forming methods on these low formability metals result in cracks, necking, or other imperfections developing in the outer surface of such metal sheets when cold angled corners or tight radii. As a result, warm forming or hot forming is typically required when forming such metals in order to prevent such unacceptable imperfections from developing along the outer bending surface of angled corners.

Such surface cracks resulting from traditional cold forming methods compromise the integrity of the part and are simply unacceptable in commercial products, including automotive applications. In other words, the inability to form a part without such unacceptable imperfections is a primary concern. Until one has been able to form an acceptable angled corner by a process, such as cold forming, a skilled artisan will not consider secondary considerations (e.g., ways to improve the repeatability or tolerances of the formed undamaged corner). Thus, a skilled artisan would not worry about managing secondary considerations, such as springback, until after it was possible to successfully cold form an acceptable angled corner.

The ability to cold forming continuous metal sheets offers many advantages. For example, a cold formed part has increased strength and hardness as a result of strain hardening. Controlling directional grain orientation resulting from cold forming enables the production of desired directional strength properties. Cold forming continuous metal sheets is the most economic manufacturing method overall because such cold forming has the highest productivity and lowest die and operational costs. Cold forming also enables more accurate geometric tolerances and better surface finishes than hot or warm forming. Cold forming additionally eliminates substantial energy requirements and the time necessary to heat the metal. Thus, the overall forming costs are significantly lower and meaningfully faster production is possible with cold forming processes.

SUMMARY

In one aspect of the present disclosure a method of incremental cold forming an angled corner in a continuous advanced high strength metal sheet includes cold forming an outer bend radius in an outer position within a final arc of the angled corner with an outer bend radius male die member. A central bend radius is cold formed in a central position spaced from the outer position and within the final arc of the angled corner with a central bend radius male die member. An inner bend radius is cold formed in an inner position spaced from the outer position and the central position and within a final arc of the angled corner with an inner bend radius male die member. The angled corner is transferred between each of the bend radius male die members using the continuous advanced high strength metal sheet.

In an additional aspect of the present disclosure at least one additional central bend radius is cold formed within the final arc of the angled corner. Each additional bend radius is located in a corresponding additional central bend radius position that is spaced from all other bend radii positions.

In another aspect of the present disclosure the cold forming the outer bend radius occurs before the cold forming the central bend radius. In addition the cold forming the central bend radius occurs before the cold forming the inner bend radius.

In a further aspect of the present disclosure at least one additional central bend radius is cold formed within the final arc of the angled corner. Each additional bend radius is located in a corresponding additional central bend radius position that is spaced from all other bend radii positions. In addition, the cold forming the outer bend radius occurs before the cold forming the central bend radius, which cold forming the central bend radius occurs before the cold forming the additional central bend radius, which cold forming the additional central bend radius occurs before the cold forming the inner bend radius.

In additional aspects of the present disclosure a roll forming apparatus is used to perform each of the cold forming and transferring operations; or a progressive die forming apparatus is used to perform each of the cold forming and transferring operations.

In further aspects of the present disclosure none of the outer, central or inner bend radii cold forming operations do result in forming an initial arched surface extending from the angled corner that is subsequently flattened; and none of the inner, outer or central bend radii are subsequently flattened, such as to account for springback.

In yet other aspects of the present disclosure the continuous advanced high strength metal sheet is an ultra-high strength steel, a magnesium alloy or a 7000 series aluminum alloy.

In yet further aspects of the present disclosure, the angled corner defines an angle that is 90 degrees, or is at least 60 degrees.

DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings.

FIG. 1 is a simplified illustration of various aspects of the example methods of incremental cold forming an angled corner in a continuous advanced high strength metal sheet in accordance with the present disclosure.

FIG. 2 is an enlarged partial cross-section view of a final angled corner formed by the example methods represented in FIG. 1.

FIG. 3 is a graph showing a comparison of outer surface strain distributions of single step cold angled corner forming operations to the example cold forming methods represented in FIG. 1.

FIG. 4 is a simplified illustration of a roll forming apparatus used to perform various roll forming exemplary cold forming methods represented in FIG. 1.

FIG. 5 is a simplified illustration of a progressive die forming apparatus used to perform various progressive die forming exemplary cold forming methods represented in FIG. 1, shown in a closed die state.

FIG. 6 is a simplified illustration of the progressive die forming apparatus of FIG. 5 shown in an open die state.

DETAILED DESCRIPTION

Further areas of applicability will become apparent from the description, claims and drawings, wherein like reference numerals refer to like features throughout the several views of the drawings. It should be understood that the detailed description, including disclosed embodiments and drawings referenced therein are merely exemplary in nature, intended for purposes of illustration only, and are not intended to limit the scope of the present disclosure.

FIGS. 1-6 illustrate and explain example methods of incremental cold forming an angled corner 20 in a continuous sheet of advanced high strength metal 22. As used herein “advanced high strength metal(s)” refers to such a metal sheet(s) with cold forming formability that prevents the continuous sheet thereof from being successfully cold formed into the desired shape, including one or more angled corners, using a single bend radii location, without causing visible surface defects. The specifically desired shape to be formed plays a role in whether a specific metal sheet comprises an advanced high strength metal in a particular situation. As disclosed herein, continuous sheets 22 of such a low formability advanced high strength metal can be successfully cold formed into the desired shape using a method in which the entire arc of the angled corner is made up of multiple partial arcs formed by multiple incremental smaller angle bending operations, each at a different bend radii spaced from each other and forming a portion of the entire arc. Exemplary advanced high strength metals of the continuous sheet 22 for typical desired shapes of the automotive industry include an ultra-high strength steel, such as a complex phase (CP) steel or a dual phase (DP) steel, a 7000 series aluminum alloy, a magnesium alloy, or another advanced high strength metal.

The steps of the example incremental bending methods can be explained with reference to the simplified illustrations of FIGS. 1 and 2. As illustrated, the continuous sheet of advanced high strength metal 22 is bent an outer incremental bend amount 26 in a cold forming operation at an outer bend radius 24. Next, the continuous metal sheet 22 is bent an outer central incremental bend amount 30 at an outer central bend radius 28 spaced inwardly from the outer bend radius 24 an outer central distance 32. Then, the continuous metal sheet 22 is bent an inner central incremental bend amount 34 at an inner central bend radius 36 spaced inwardly from the outer central bend radius 28 an inner central distance 38. The continuous metal sheet is next bent an inner incremental bend amount 40 at an inner bend radius 42 spaced inwardly from the inner central bend radius 36 an inner distance 43.

In the illustrated 90 degree angled corner 20, the outer incremental bend amount 26 can correspond to an arc or angle of 20 degrees; the outer central incremental bend amount 30 can correspond to an arc or angle of 25 degrees; the inner central incremental bend amount 34 can correspond to an arc or angle of 25 degrees; and the inner incremental bend amount 40 can correspond to an arc or angle of 20 degrees. Many alternative incremental bend amounts for a 90 degree angled corner are possible. For example, these bend amounts are alternatively 20 degrees, 20 degrees, 20 degrees, and 30 degrees, respectively. In other alternatives, only three spaced apart bend radii are used, or more than four spaced apart bend radii are used. Alternatives to the 90 degree angled corner are possible, and include 60, 70, and 80 degree angled corners 20 among others.

As illustrated in FIG. 2, each of the relevant bend radii is positioned within the boundaries of the overall arc (represented by the dotted lines) of the final angled corner 20. Thus, the available overall distance or space between the various bend radii (total of distances 32, 38, 42) depends upon the length of the overall arc, radius or sharpness of the final angled corner 20. In some aspects, the distances 32, 38, 43 are all the same. Alternatively, any of the distances 32, 38, 43 are different from each other. It is worth noting that the drawings herein are provided to explain the concepts but are not drawn to scale. For example, the relationship between the overall arc size or length and the distances 32, 38, 43 between the bend radii in FIG. 1 are such that these distances are exaggerated and/or that the overall arc length of the angled corner is underrepresented.

The believed reason the disclosed incremental bending cold forming process of advanced high strength metal works can be explained with reference to FIG. 3. As shown on the left side of FIG. 3, when such a metal sheet 22 is bent fully at a single bend radius, the strain limit at the outer surface is exceeded due to the relatively low ductility of such metal sheets 22. When this happens, cracks, necking, or other defects occur in the stretched outer surface along the length of the angled corner 20. In contrast, when multiple spaced apart bend radii 24, 28, 36, 42 are used, the surface strain is spread across a corresponding distance or space of the outer surface of the metal sheet 22. This means no individual part of the outer surface of the metal sheet 22 experiences the full magnitude of the strain associated with forming the angled corner 20, allowing the surface strain to remain under the surface strain limit.

As illustrated in FIGS. 4-6, the example processes includes transferring the angled corner 20 being formed between each of corresponding bend radii male forming die members 44, 46, 48, 50 using the continuous advanced high strength metal sheet 22. Specifically, in the example of FIG. 4, the various cold forming and transferring operations are accomplished using a roll forming apparatus 52 and process. As illustrated, an overall lateral width 54, 56, 58, and 60, respectively, between the bend radii of each male forming member 44, 46, 48, 50 of each roller pair gets progressively narrower in order to form the series of spaced apart bend radii 24, 28, 36, 42 for each of the adjacent corners 20. Thus, the continuous sheet 22 is used to transfer the angled corner 20 being formed between the various roller pairs of the roll forming apparatus 52.

In the example of FIGS. 5 and 6, the various cold forming and transferring operations are accomplished using a progressive die forming apparatus 62 process. As with the roll-forming apparatus of FIG. 4, an overall lateral width 54, 56, 58, and 60, respectively, of each male forming member 44, 46, 48, 50 of each forming station pair gets progressively narrower in order to form the series of spaced apart bend radii 24, 28, 36, 42 for each of the adjacent corners 20. As with the roll-forming example, each angled corner 20 being formed remain attached to the continuous sheet 22 until the angled corner 20 is fully formed. Thus, a portion of the continuous sheet 22 extending between the series of angled corners 20 being formed remains coupled to each part and is used to transfer the angled corner 20 being formed between the various forming station die pairs.

In the example cold angled corner forming processes above, there is no need to form an arched surface adjacent the angled corner 22 that is being formed, or to subsequently flatten such an initial arched surface as part of the angled corner forming process. Similarly, there is no need in the example cold angled corner forming processes above to flatten any of the bend radii 24, 28, 36, 42 after forming them in order to account for springback. Although in alternative examples such bend radii flattening activities may additionally occur with respect to additional bend radii, at least three, four, or more bend radii positioned within the overall arc of the final angled corner are formed that are not subsequently subjected to any such bend radii flattening.

The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention. 

1. A method of incremental cold forming an angled corner in a continuous advanced high strength metal sheet, the method comprising: cold forming an outer bend radius in an outer position within a final arc of the angled corner of the continuous advanced high strength metal sheet with an outer bend radius male die member; cold forming a central bend radius in a central position spaced from the outer position and within the final arc of the angled corner of the continuous advanced high strength metal sheet with a central bend radius male die member; cold forming an inner bend radius in an inner position spaced from the outer position and the central position and within a final arc of the angled corner of the continuous advanced high strength metal sheet with an inner bend radius male die member; utilizing a progressive die forming apparatus to perform each of the cold forming and transferring operations; and transferring the angled corner between each of the bend radius male die members by manipulating the continuous advanced high strength metal sheet; wherein the cold forming the outer bend radius occurs before the cold forming the central bend radius, which cold forming the central bend radius occurs before the cold forming the inner bend radius.
 2. The method of incremental cold forming an angled corner in a continuous advanced high strength metal sheet of claim 1, further comprising cold forming at least one additional central bend radius within the final arc of the angled corner, each additional bend radius being located in a corresponding additional central bend radius position that is spaced from all other bend radii positions.
 3. (canceled)
 4. The method of incremental cold forming an angled corner in a continuous advanced high strength metal sheet of claim 1, further comprising cold forming at least one additional central bend radius within the final arc of the angled corner, each additional bend radius being located in a corresponding additional central bend radius position that is spaced from all other bend radii positions, wherein the cold forming the outer bend radius occurs before the cold forming the central bend radius, which cold forming the central bend radius occurs before the cold forming the additional central bend radius, which cold forming the additional central bend radius occurs before the cold forming the inner bend radius.
 5. (canceled)
 6. (canceled)
 7. The method of incremental cold forming an angled corner in a continuous advanced high strength metal sheet of claim 1, wherein none of the outer, central or inner bend radii cold forming operations result in forming an initial arched surface extending from the angled corner that is subsequently flattened.
 8. The method of incremental cold forming an angled corner in a continuous advanced high strength metal sheet of claim 1, wherein none of the outer, central or inner bend radii are subsequently flattened to account for springback.
 9. The method of incremental cold forming an angled corner in a continuous advanced high strength metal sheet of claim 1, wherein the angled corner defines an angle that is at least 60 degrees.
 10. The method of incremental cold forming an angled corner in a continuous advanced high strength metal sheet of claim 1, wherein the metal sheet is an ultra-high strength steel.
 11. The method of incremental cold forming an angled corner in a continuous advanced high strength metal sheet of claim 1, wherein the metal sheet is one of a 7000 series aluminum alloy and a magnesium alloy. 